This present invention relates in general to plant molecular biology and more particularly to a method for controlling the ripening of fruit and vegetables as well as controlling the effects of senescence in plants and recombinant DNA molecules capable of affecting the desired control.
The following background information has been reproduced from U.S. Pat. No. 5,512,466.
One of the major problems facing the fruit, vegetable and cut flower industry is the loss of a considerable amount of goods due to spoilage. It is estimated that 12 to 20 percent of the fruit and vegetable products become spoiled from the time they leave the farm until they get to the retail or processing outlets. In the cut flower industry, senescence (the wilting or dying) of the flower before it can be effectively marketed is a significant problem. The spoiling or senescence process observed in fruits, vegetables and cut flowers results in a number of undesirable problems. Chief among these problems is the short harvesting season for the goods and the short shelf life of the goods following the harvest. Furthermore, these spoilage losses ultimately result in a higher cost of the goods to the consumer.
A primary cause of the spoilage of fruits and vegetables is the natural ripening process of the fruit or vegetable. As the fruit or vegetable becomes more ripe it becomes softer and more easily bruised and susceptible to disease or other spoilage causing agents. It is known that ethylene production in the plant stimulates the fruit ripening process and is the key component in the ripening of fruits and vegetables. Ethylene also accelerates flower and leaf senescence. Senescence of flowers treated with the ethylene antagonist STS (silver thiosulfate) was markedly delayed (reviewed in Plant Physiology ed. Tasz, Zeigen 1998) and in Wang and Woodson 1989 Plant Physiology 89: 434-438. Others have attempted to control the ripening of fruits and vegetables in an attempt to extend the shelf life and/or harvesting season of the goods. Many of these attempts have been topical applications of chemicals to the fruit or vegetable itself. These chemical solutions have involved direct applications to the plant in the field or post-harvest applications to the fruit or vegetable itself. Several of these methods are discussed in U.S. Pat. No. 4,957,757 or U.S. Pat. No. 4,851,035. Due to the increasing importance of reducing additional stresses on the environment, a non-chemical means for controlling ripening would be advantageous and beneficial to the industry.
More recently, researchers have used a molecular biology approach to block ethylene synthesis in plants in an attempt to control the ripening of tomatoes. This approach involved transforming a tomato plant with an antisense gene that inhibited the synthesis of ethylene. The antisense gene produces (-) strand RNA that lowers the steady state levels of the (+) strand mRNA encoding a polypeptide involved in the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by the ethylene forming enzyme ACC oxidase (Hamilton, A., Lycett, G. and Grierson, D. (1990). Antisense gene that inhibits synthesis of the hormone ethylene in transgenic plants. Nature 346:284-287). While this method exhibits some degree of utility, it would be neither easy nor efficient to apply this technology to other plants, because the antisense gene would probably be species and gene specific which would entail obtaining a different antisense gene for each species of plant desired to be transformed.
Similarly, shutting down of ACC synthase, which is the key enzyme of ethylene biosynthesis that catalyses the production of the immediate precursor of ethylene, ACC from S-adenosyl methionine, by using antisense transcript to inactivates the "sense transcript" caused a significant reduction in ethylene biosynthesis and inhibition of fruit ripening (Oeller et al (1991) Science 254: 437-439; Picton et al. Plant J. 3: 469-481 1993).
A more universal method for controlling the ripening of fruits and vegetables as well as a method for controlling senescence of plant tissue is disclosed in U.S. Pat. No. 5,512,466. The method generally embraces the expression of an ACC metabolizing enzyme in the fruit or other desired plant tissue to inhibit the production of ethylene in the fruit or plant tissue. The use of the ACC metabolizing enzyme ACC deaminase is described in detail. The ripening or senescence process in the fruit or plant tissue is inhibited by the expression of the ACC deaminase gene such that the shelf-life and marketability of the fruit or plant is enhanced. The ACC metabolizing enzyme may be used in combination with other methods for reducing ethylene production in transformed plants to further reduce the production of ethylene in the fruit or plant. DNA constructs containing the ACC deaminase gene are also described.
Yet another, novel, more efficient and more universal approach for controlling the ripening of fruits and vegetables, as well as for controlling senescence of plant tissue, would be the expression of a catalytic antibody capable of metabolizing a precursor participating in the synthetic pathway of ethylene in the fruit or other desired plant tissue to inhibit the production of ethylene in the fruit or plant tissue.
There is thus a widely recognized need for, and it would be highly advantageous to have, a catalytic antibody capable of metabolizing a precursor participating in the synthetic pathway of ethylene and genetically modified plants expressing same for controlling the ripening of fruits and vegetables, as well as for controlling senescence of plant tissue.